1. Field of the Invention
This invention relates to delta-sigma analog-to-digital (A/D) converters for imaging systems and, more particularly, to apparatus that partitions an A/D converter of an ultrasonic imaging system, with one portion located in the sensor or transducer probe and the other in the signal processor or imaging console.
2. Description of the Related Art
An ultrasonic imaging system requires a large array of ultrasonic transducers contained within a hand-held probe to provide steering and focusing of the ultrasonic beam. The hand-held probe is placed in contact with the patient's skin and must be capable of being manipulated freely by the operator. Each transducer receives, from the object being examined, a high frequency signal that must be transmitted back to the host electronics system or imaging console for signal processing.
The probe constraints, namely a large number of transducers combined with ease of maneuverability, require that cabling which connects the probe to a console be small and flexible and that total power dissipated in the probe be kept as low as possible.
At the same time, there are advantages to converting the sensor output signals to digital form before they are processed. This creates a need for an analog-to-digital (A/D) converter architecture exhibiting the least possible power dissipation at the sensor location.
Moreover, there exists a constraint on the dynamic range and preservation of accuracy of the signals from each of the transducer elements so that accurate beamforming can be accomplished. Active imaging systems such as radar, sonar, and ultrasound systems, however, require very large dynamic ranges since reflections from nearby objects are generally of much larger amplitude than reflections from objects further away. These various constraints discussed above become incompatible when the probe contains more than about 100 transducers.
In light of the foregoing, there exists a need for A/D converter architecture that preserves the accuracy and dynamic range of a large number of signals conducted in close proximity in a small, flexible cable, with little, power dissipation at the probe head.
There also exists a need for A/D converter architecture that does not require critical component matching while using optical links that have relatively low dynamic range in which almost all of the power dissipation takes place at the remote end of the optical links.
There exists a further need for A/D converter architecture that has a dynamic range at a signal source that is substantially larger than that of a signal-carrying link that communicates with a sensor.